The present invention relates to a printing apparatus having a daisy-shaped type wheel, and more particularly to a printer of such type in which the type wheel is changeable without having to remove an inked ribbon or a ribbon cartridge.
On a printer equipped with a daisy-shaped type wheel which has a multiplicity of radially disposed type element holders each carrying at its outer end a type element, the type wheel is coupled directly with a rotor shaft of an electric drive motor and rotated continuously or intermittently in a vertical plane to select a type element into position. A selected type element which has been located at the substantially top position of the type wheel is striken by a print hammer against a sheet of paper over a platen via an inked ribbon. The inked ribbon is either held at a height of the type element to be striken, or carried to that height only when the printing action is performed from its lower non-printing position.
It is generally recognized that type elements that can be provided on one type wheel are limited in number, that is, it is impossible to provide type elements of all required characters on a single type wheel. It is also recognized that a type wheel is locally worn out or damaged during years of service. These facts suggest the necessity of changing a type wheel as needed. For the change of type wheels, the following two methods are available.
The first method is practiced by pivoting an entire printing head which carries integrally the motor, type wheel, print hammer, ribbon cartridge, etc., so that the type wheel is placed in a plane 45 degrees inclined upwardly from the horizontal plane, before the type wheel is mounted or removed in an axial direction of the rotor shaft of the drive motor. In changing a type wheel with this method, the ribbon may be an obstruction to the type wheel being changed and thus the ribbon cartridge must be removed before the type wheel is changed.
Another method is used when a printer uses a type wheel which is encased within a cartridge such that a limited number of the type elements are exposed toward the platen. In this method, the drive motor or only the rotor shaft portion is first retracted to the rear and the type wheel and its cartridge are then mounted or removed in the direction normal to the axis of the rotor shaft. Although this second method eliminates the need of removing a ribbon cartridge before mounting or removing a type wheel, it requires a cartridge for guiding the type wheel to the correct mounting position, and a type wheel cartridge guiding and supporting mechanism, preferably a highly reliable, considerably complicated mechanism that is capable of guiding the type wheel to its exact mounting position on the rotor shaft a visible access to which is not obtainable.